Man-machine interfaces using a haptic technology based on the recognition of sound waves propagating through an interface plate, present multiple advantages with respect to the touch control man-machine interfaces based on standard technologies, like capacitive interfaces. In particular, the material of the interface plate on which a user creates an impact, does not need to be conductive using the acoustic technology and furthermore the way the impact is created is not limited, as an acoustic sound wave can be generated by any means, e.g. being the finger tip, a gloved finger, a stylus etc.
In fact, a tap on an object produces a sound wave pattern through the material creating an acoustic signature which is unique to the location of the impact. An acoustic sensor linked to a computer or a Digital Signal Processing (“DSP”) board will capture the audio vibrations within the object, generating a corresponding acoustic signature. This technology is described in WO 03—107261A2.
Up to now the technology was adapted to identify the location of one tap on the interface means at a time and to initiate the corresponding action as a function of the identified location of the tap or impact. However, modern applications are demanding man-machine interfaces having the possibility to identify the locations of multiple simultaneous inputs and/or tracking inputs corresponding to the sliding of an input means on the interface means to thereby offer more user friendliness and/or enhanced capabilities.